The present invention relates to an elongate structure of tetrahedral elements linearly arranged between a fixed end and a free end. Each element has two pairs of triangular faces, each pair of faces meeting at an edge which is connected to an edge of an adjacent tetrahedral element.
U.S. Pat. No. 3,237,362, incorporated herein by reference, describes a structural unit of this general type, in which a tubular blank is collapsed at regular intervals from diametrically opposite sides to form crimped sections which separate the tetrahedral elements. While bending at the crimped sections may be undertaken during manufacture to obtain a desired final shape, flexibility in use is not suggested. On the contrary, the nodes at the ends of the crimped sections may be tied by welding chordal rods to assure that the structure remains rigid.
The prior art structural unit has the characteristics of a structural skin system and retains all the torsional resistance of a tube. Applied external loads are distributed in all directions, thus reducing the high stresses in the directly loaded parts.
It would be desirable to retain the advantages of the prior art structural unit in a structure in which the shape could be readily changed.